The Supreme Court’s decision brings some much-needed clarity to the issue of whether a trial judge can disqualify an expert based on impartiality and lack of independence at the qualification stage (i.e., Mohan). Until now, there has been conflicting case law on this issue, with the majority of the cases supporting the conclusion that, at a certain point, expert evidence should be ruled inadmissible due to the expert’s lack of impartiality and/or independence.

The important questions that remained unanswered, and that trial courts struggled with, were (1) should the elements of an expert’s duty (i.e., independence and impartiality) go to admissibility of the evidence rather than simply to its weight? (2) If so, is there a threshold admissibility requirement in relation to independence and impartiality?

The Supreme Court unanimously answered both questions with “yes.”

(1) The Expert’s Duty

The Supreme Court stated that expert witnesses have a duty to the court to give fair, objective and non-partisan opinion evidence. They must be aware of this duty and be able and willing to carry it out. Underlying the various formulations of the duty of an expert are three related concepts:

(i) Impartiality: The expert’s opinion must be impartial in the sense that it reflects an objective assessment of the questions at hand.

(ii) Independent: It must be independent it in the sense that it is the product of the expert’s independent judgment, uninfluenced by who has retained him or her or the outcome of the litigation.

(iii) Absence of Bias: It must be unbiased in the sense that it does not unfairly favour one party’s position over another. The “acid test” is whether the expert’s opinion would not change regardless of which party retained him or her.

However, the Supreme Court recognized that these concepts must be applied to the realities of adversary litigation. Experts are generally retained, instructed and paid by one of the adversaries. According to the Court, “these facts alone do not undermine the expert’s independence, impartiality and freedom of bias.”

(2) The Framework

The Court concluded that concerns related to the expert’s duty to the court and his or her willingness and capacity to comply with it are best addressed at the “qualification of expert” element of the Mohan framework (which is part 4 of that test). A proposed expert witness who is unable and unwilling to fulfill his or her duty to the court is not properly qualified to perform the role of an expert. If the expert witness does not meet this threshold admissibility requirement, his or her evidence should not be admitted. Once this threshold is met, however, remaining concerns about an expert witness’s compliance with his or her duty should be considered as part of the overall cost-benefit analysis which the judge conducts to carry out his or her gatekeeping function.

The Supreme Court essentially adopted the 2-part test set out by the Ontario Court of Appeal in R. v. Abbey (2009 ONCA 624) and added its own gloss with respect part 4 of that test:

Step 1

The proponent of the expert evidence must establish the threshold requirements of admissibility. These are the four Mohan factors (relevance, necessity, absence of an exclusionary rule, and properly qualified expert).

In addition, in the case of an opinion based on novel or contested science or science used for a novel purpose, the reliability of the underlying science for that purpose (see R. v. J.-L.J. (2000 SCC 51) per Binnie J.).

After reviewing Canadian, British, Australian, and U.S. authorities, the Supreme Court concluded that an expert’s lack of independence and impartiality goes to the admissibility of the evidence in addition to being considered in relation to the weight to be given to the evidence if admitted. In reaching this conclusion, it relied upon Justice Binnie’s oft cited quote in R. v. J-L.J.: “The admissibility of the expert evidence should be scrutinized at the time it is proffered, and not allowed too easy an entry on the basis that all of the frailties could go at the end of the day to weight rather than admissibility”.

The Court concluded that concerns related to the expert’s duty to the court and his or her willingness and capacity to comply with it are best addressed initially in the “properly qualified expert” element of the Mohan framework. In another recent decision, the Supreme Court held that for expert testimony to be inadmissible, more than a simple appearance of bias is necessary. The question is not whether a reasonable person would consider that the expert is not independent. Rather, what must be determined is whether the expert’s lack of independence renders him or her incapable of giving an impartial opinion in the specific circumstances of the case (Mouvement Laïque Québécois v. Saguenay (City) (2015 SCC 160) at para. 106).

Evidence that does not meet these threshold requirements should be excluded.

Step 2

Finding that expert evidence meets the basic threshold does not end the inquiry. At the second discretionary gatekeeping step, the judge balances the potential risks and benefits of admitting the evidence in order to decide whether the potential benefits justify the risks (put another way, whether otherwise admissible expert evidence should be excluded because its probative value was overborne by its prejudicial effect). This is a residual discretion to exclude evidence based on a cost-benefit analysis. The Court adopted Doherty J.A.’s summary of this balancing exercise in Abbey – that the “trial judge must decide whether expert evidence that meets the preconditions to admissibility is sufficiently beneficial to the trial process to warrant its admission despite the potential harm to the trial process that may flow from the admission of the expert evidence.”

(3) The Threshold

The Court also discussed the appropriate threshold for admissibility. If a witness is unable or unwilling to fulfill his or her duty, they do not qualify to perform the role of an expert and should be excluded. The expert witness must, therefore, be aware of this primary duty to the court and be able and willing to carry it out. While the Court wouldn’t go so far as to hold that the expert’s independence and impartiality should be presumed absent challenge, the Court did state that absent such challenge, the expert’s attestation or testimony recognizing and accepting the duty will generally be sufficient to establish that this threshold is met.

Once the expert testifies on oath to this effect, the burden is on the party opposing the admission of the evidence to show that there is a realistic concern that the expert’s evidence should not be received because the expert is unable and/or unwilling to comply with that duty. If the opponent does so, the burden to establish on a balance of probabilities this aspect of the admissibility threshold remains on the party proposing to call the evidence. If this is not done, the evidence, or those parts of it that are tainted by a lack of independence or by impartiality, should be excluded.

The Court held that this threshold requirement is not particularly onerous and it will likely be quite rare that a proposed expert’s evidence would be ruled in admissible for failing to meet it. The trial judge must determine, having regard to both the particular circumstances of the proposed expert and the substance of the proposed evidence, whether the expert is able and willing to carry out his or her primary duty to the court. It is the nature and extent of the interest or connection with the litigation or a party thereto which matters, not the mere fact of the interest or connection. The Court further stated that the existence of some interest or a relationship does not automatically render the evidence of the proposed expert inadmissible. For example, a mere employment relationship with the party calling the evidence will be insufficient to do so.

The Court went on to provide some examples of types of interests/relationships that may warrant exclusion of the expert’s evidence:

A direct financial interest in the outcome of the litigation will be of some concern;

A very close familial relationship with one of the parties;

Situations in which the proposed expert will probably incur professional liability if his or her opinion is not accepted by the court; or

An expert who, in his or her proposed evidence or otherwise, assumes the role of an advocate for a party.

The decision as to whether an expert should be permitted to give evidence despite having an interest or connection with the litigation is a matter of fact and degree. The concept of apparent bias is not relevant to the question of whether or not an expert witness will be unable or unwilling to fulfill its primary duty to the court. When looking at an expert’s interest or relationship with a party, the question is whether the relationship or interest results in the expert being unable or unwilling to carry out his or her primary duty to the court to provide fair, non-partisan and objective assistance.

The Court emphasized that exclusion at the threshold stage of the analysis should occur only in very clear cases in which the proposed expert is unable or unwilling to provide the court with fair, objective and non-partisan evidence. Anything less than clear unwillingness or inability to do so should not lead to exclusion, but be taken into account in the overall weighing of costs and benefits of receiving the evidence.

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